The present invention relates to a screw and, more particularly, to a screw adapted to be used in wood, construction materials, and similar materials.
A large amount of wood or compound wooden materials mixed and compressed from plastic resin and wood chips are used to produce wooden work-pieces for furniture, decoration and construction, and screws are often used in connection between wooden work-pieces.
A conventional screw 10 for using with wood is shown in FIG. 1. The screw 10 includes a round shank 12 and a thread 14 disposed on the shank 12. The shank 12 includes an insertion end 16 and a head end 17. The insertion end 16 has an end cutting groove 18. When the screw 10 is screwed into a to-be-connected work-piece with the insertion end 16, the end cutting groove 18 is used for cutting the work-piece, so that the thread 14 can be screwed into the work-piece smoothly. However, because the cross section of the shank 12 of the screw 10 in FIG. 1 is round, a relatively larger friction force is produced from the full contact between the thread 14 and the work-piece when the thread 14 is screwed into the work-piece, which will require more effort and time in operation. Furthermore, the end cutting groove 18 of the screw 10 extends axially along the shank 12, making it difficult for wood chips produced from cutting to be expelled smoothly. Therefore, the screw 10 is obstructed by the waste chips during the process of screwing into the work-piece, which will require more effort in operation, and the work-piece will easily crack because of compression. Additionally, when the screw 10 is used for screwing into compound sheets mixed and compressed from plastic resin and wood chips, the waste chips can not be effectively cut off, because the end cutting groove 18 of the screw 10 extends axially along the shank 12, and because obstructions will be produced when the screw 10 is screwed into the compound sheets.
Conventional screws 10a and 10b used for screwing into compound sheets mixed and compressed from plastic resin and wood chips are shown in FIGS. 1A and 1B respectively. Each of the screws 10a and 10b includes a shank 12 and a thread 14 disposed on a lower section of the shank 12. The shank 12 includes an insertion end 16 and a head end 17. Furthermore, the thread 14 of the screw 10a in FIG. 1A near the insertion end 16 has a smaller thread height favorable for screwing into the compound sheet surfaces. V-shaped grooves 19 are disposed in the thread 14 favorable for the expelling of waste chips produced from the screwing of the screw 10a. However, the speed of screwing of the screw 10a into the compound sheets is relatively slow. Specifically, the thread convolutions with smaller thread height are designed for allowing the screw 10a to screw into the compound sheets slowly, so that there is more time for the waste chips to be expelled. Additionally, the V-shaped grooves 19 of the screw 10a can not effectively cut off the waste chips. As for the screw 10b in FIG. 1B, even though the screw 10b can be screwed into the compound sheets with faster speed, the thread 14 of the screw 10b can not effectively cut off the waste chips. As a result, the screw 10b will be obstructed by the waste chips when it is screwed into the work-piece, and the compound sheets will, therefore, crack easily.